Make sure the tool supports your learning objectives. Be purposeful in your decision to choose a specific tool.
Explain the tool to the students including why you are using it, how it will enhance their learning, how to use it, and privacy options available to them.
When evaluating a tool think about how easy it is to use, if it is it free, what is the minimum technology necessary to use it, is it linkable or embeddable, are their privacy options, and is it appropriate for educational purposes.
Look to see if there is an educator account.
Don't be afraid to try new things or to fail. It's ok to fail.
Don't overwhelm students with too many different tools.
Provide examples for students to look at.
For semester long classes, introduce students to the tool early in the semester so they can get their toes wet before they have to use it for a major end-of-semester assignment.
Web 2.0 tools are not covered by FERPA laws. Include a FERPA waiver for those tools in the syllabus for the students to electronically sign.
An online whiteboard app that lets you use your computer, tablet or smartphone to easily draw sketches, collaborate with others and share them with the world.